The present invention relates to an atherectomy catheter for removing an occlusive material stenosing or occluding lumens of tubular organs.
Atherosclerosis is caused by precipitation of fatty acid inside a lower side of the inner membrane layer of a blood vessel. Conceivably, comparatively soft fatty acid deposits initially at the lower side of the inner membrane layer. With the passage of time, a cholesterol component is captured into the deposited fatty acid to form a calcified atheroma layer. The inside of the blood vessel has a stenosed state or an occluded state owing to the formed atheroma layer. Thereby a bloodstream is interrupted. If this state is left, angina, myocardial infarction occur in the case of the heart, and necrosis of finger tissues of hands and legs and intermittent claudication in the case of the limbs.
Atherectomy means a procedure for removing a developed arteriosclerotic layer from the blood vessel by a catheter. Normally, only the atherectomy is not performed but carried out in combination with a balloon angioplasty. Further to maintain a lumen formed by the removal of the arteriosclerotic layer and the angioplasty, a stent placement is performed. Even if such a procedure is performed, a new arteriosclerotic layer may develop at the inner side of a stent as pointed out in many research reports. In this case, the atherectomy, the balloon angioplasty, and the stent placement are often performed. Recently researches are made to decrease a stenosis rate by the drug eluting stent expected to have the effect of preventing hyperplastic arteriosclerosis.
The atherectomy may be performed to treat chronic occlusion in which a bloodstream is completely interrupted. In some cases, as the amount of the bloodstream becomes smaller, the inner membrane of the blood vessel grows increasingly large. Various techniques for treating these lesions are disclosed.
For example, in the technique disclosed in WO01/74255, the rotor is expandable and contractible. By utilizing the expandability and contractibility of the sheath means functioning as the rotor, the sheath means is repeatedly pushed into a desired portion inside the blood vessel and pulled therefrom until a inner diameter of a blood vessel is dilated.
A thrombus is another cause of occluding the blood vessel. In some cases, the thrombus generated by a bleed of a blood vessel flows to a periphery and deposits thereon. The surface of the atheroma layer is liable to be damaged. Thus when the surface of the atheroma layer is damaged for some reason, platelets in circulating blood may agglutinate to form the thrombus. As a result, the blood vessel is occluded. In some cases, the thrombus is present together with the atheroma layer. Techniques of removing the deposited thrombus by using a balloon have been used for a long time.
In the catheter described in WO01/74255, it is necessary to perform the operation of penetrating the distal end-closed basket-shaped sheath means (shear member) into a lesion of a developed arteriosclerotic layer or a lesion stenosed or occluded with the thrombus. It is also necessary to repeatedly perform the operation of pushing or pulling the sheath means by rotating the sheath means until the inner diameter of the blood vessel is dilated.
But in a lesion close to occlusion or an occluded lesion, it is difficult for a contrast media to flow therein even in an examination by fluoroscopy. Thus it is difficult to discriminate a portion of the lesion to which the sheath means is approached. It is also difficult to correctly penetrate the sheath means through the lesion. Thus the sheath means is liable to damage the blood vessel or break therethrough. As described above, the catheter described in WO01/74255 necessitates an operator to take much time and labor and become skilled.
It is an object of the present invention to provide an atherectomy catheter capable of easily, rapidly, securely, and safely removing an occlusive material from a stenosed or occluded lumen of a tubular organ.